Accurately reporting the traffic condition by providing alarm information (such as road traffic information) with appropriate content at appropriate time is useful for the driver to comfortably and safely drive the vehicle. Congestion status of road, road regulation status due to an occurrence of accident or implementation of construction, road surface condition, and weather condition (for example, temperature and visibility) are typical useful road traffic information.
One of the road traffic information providing systems recently being developed is a road traffic information providing system using DSRC (Dedicated Short Range Communications) for providing road traffic information to a driver and the like of a vehicle mounted with an ETC vehicle-mounted device (for example, see Patent Document 1).    Patent Document 1: Japanese Patent Application Laid-Open No. 2005-258726